Apparatus and method for propelling vehicles in space



Oct. 18, 1966 A. c. DUCATI 3,279,177

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A. C. DUCATI Oct. 18, 1966 APPARATUS AND METHOD FOR PROPELLING VEHICLES IN SPACE Filed June 1.0, 1965 :5 Sheets-Sheet 2 CUE'E/VT 500865 BAZA/VCE MfA/VS INVENTOR. AQQ/A/VO CI 06,477

BY dw ATTOQ/VIQG A. C. DUCATI APPARATUS AND METHOD FOR PROPELLING VEHICLES IN SPACE Filed June L0, 1963 3 Sheets-Sheet 5 IN VEN TOR. 402/4/1/0 6. 0064 7/ United States Patent 3,279,177 APPARATUS AND METHOD FOR PROPELLING VEHICLES IN SPACE Adriano C. Ducati, Santa Ana, Calif., assignor to Giannini Scientific Corporation, New York, N.Y., a corporation of New York Filed June 10, 1963, Ser. No. 286,608 21 Claims. (Cl. 60203) This invention relates to a nozzle, and to an improved means for heating the gas passed therethrough. The invention also relates to a method and apparatus for propelling vehicles in space.

Since resistance heating is known to be much more efiicient than arc heating, certain workers in the field of space propulsion have attempted to conserve energy by creating resistance-type thrusters. However, thrusters of the resistance-heating type, and which are known to the present applicant, have been characterized by the presence of elongated, thin resistor elements. Such elements inherently result in disuniform heat distribution and consequent melting at isolated hot spots. In particular, hot spots are likely to develop at the ends of the resistor, due to crystallization and other effects. Furthermore, such elongated heating elements are inherently fragile and are subject to excessive erosion as their melting points are approached.

It is, therefore, one object of the present invention to provide a method and apparatus for achieving resistance heating of a gas by means of massive elements which are not subject to the generation of hot spots, which are highly resistant to erosion despite a relatively close approach to their melting points, and which produce a highly efficient heating of the gas without substantial internal heating of the resistance element.

In accordance with another of its aspects, the present invention relates to a particular type of nozzle which is characterized by an optimum ratio between the crosssectional flow area at the throat and at the nozzle mouth or discharge, such ratio being achieved despite the fact that the nozzle is extremely short. This is contrary to the concepts adhered to by numerous prior-art workers who believed that relatively long nozzles were necessary in order to achieve optimum area ratios. Furthermore, at least in those instances where the gas passed into the nozzle was in dissociated form, such workers believed that long nozzles were desirable in order that the gas would recombine therein and thereby add energy to the discharge.

A further object of the present invention is to provide a combination resistance heater and nozzle which is highly efficient in operation, not only because of the manner of heating is superior to prior-art methods but also because heating is continued until the last instant prior to discharge through the divergent section of the nozzle, and further because the divergent section is extremely short and therefore not subject to substantial frictional and other losses.

A further object of the invention is to provide a resistance heater of the contact-resistance type, in combination with an annular nozzle having a high ratio of discharge (outlet) area to throat area, and characterized by See a very short distance between the throat and the discharge end of the nozzle.

A further object of the invention is to provide a contact-resistance gas heater wherein the contact resistances between large numbers of elements are arranged in seriescircuit relationship, whereby the voltage delivered to the resistors may be made relatively high without effecting burning thereof, and the current may be relatively small and thus readily generated.

A further object of the invention is to provide a method and apparatus for creating a desired optimum contact pressure between two elements of a contact-resistance gas heater.

A further object of the invention is to provide a method and appartaus for eifecting both contact-resistance heating and are heating of gas delivered to the discharge nozzle of a thruster, the arrangement being such that a relatively high temperature may be achieved in an efficient manner.

A further and highly important object is to provide a method of space propulsion, which method involves the discharge of a dissociated gas completely through a nozzle.

These and other objects will become apparent from the following detailed description taken in connection with the accompanying drawings, in which:

FIGURE 1 is a schematic longitudinal central sectional view illustrating a thruster embodying an annular nozzle, .and also embodying means for effecting contact-resistance heating of the gas delivered to the throat of such nozzle;

FIGURE 2 is an end view showing the discharge end of the nozzle;

FIGURE 3 is a transverse sectional view taken on line 33 of FIGURE 1;

FIGURE 4 is a highly enlarged fragmentary sectional view in the region indicated by the number 4 in FIGURE 1, and showing the interface region between the two electrically-conductive contact elements;

FIGURE 4:: is an enlarged fragmentary section on line 4a4a of FIGURE 1, showing the throat of the nozzle;

FIGURE 5 is a logitudinal central sectional view of an apparatus corresponding to that shown in FIGURE 1, and schematically illustrating a means for achieving optimum contact pressure between the contact elements;

FIGURE 6 is a longitudinal central sectional view illustrating a substantial number of contact elements arranged in such manner that the contact resistances are in seriescircuit relationship;

FIGURE 7 is a transverse sectional view taken on line 77 of FIGURE 6; and

FIGURE 8 is a longitudinal central sectional view illustrating a thruster in which the gas delivered to the discharge nozzle is heated by both resistance and arc means, whereby a higher temperature may be achieved but in a manner which is less eflicient than in the case where heating is solely by resistance means.

Referring first to the embodiment shown in FIGURES 1-4, inclusive, the thruster is illustrated to comprise first and second contact elements 10 and 11 which are in surface engagement with each other along an interface region 12, means to pass gas through said interface region, and

means 14 to effect fiow of current through the contact elements and 11 and across the region 12 to thereby effect contact-resistance heating of the gas. The gas is thus heated during the entire time it travels to a discharge nozzle 15 of an annular type to 'be described in detail subsequently.

Contact element 10 is shaped as a hollow cone, whereas element 11 is a conical plug the taperangle of which corresponds to that of the element 10. A plate 16 is mounted over the wide end of the cone, so that a chamber 17 is defined therein. Gas is introduced into such chamber from a source 18, by means of conduit 19.

The current source 14 is indicated schematically, and may comprise any suitable source of direct or alternating current, single or multi-phase. The source is connected through a lead 20 to the hollow cone 10, and through a second lead 22 to the conical plug 11. The lead 22 passes through an insulator 23 which is sealingly provided in plate 16.

It is to be understood that the interface region 12 creates very close to a dead short across the current source 14, so that the voltage supplied by such source should be relatively low in order to prevent melting of any portion of either contact element at the interface. The voltage, for example, may be on the order of a fraction of a volt to a few volts, whereas the current flow may be on the order of hundreds or thousands of amperes. The leads 20 and 22 may be extremely large and highly conductive, to minimize heat losses therein.

The gas pressure delivered to the chamber 17 from source 18 should be high, such as hundreds or thousands of pounds per square inch, in order to effect a substantial flow of gas through the interface region 12. The resistance which the interface region presents to flow of gas from source 18 to nozzle 15 depends not only upon the contact pressure but upon the degree of smoothness of the mating surfaces. The surfaces are preferably relatively rough, and may be provided with small striations if desired. For example, the surfaces may be sandblasted to create the somewhat roughened appearance indicated in FIGURES 4 and 411, it being understood that the showings of these figures are enlarged or exaggerated.

The resistance to flow of gas, and also the electrical resistance presented may be varied by adjusting the pressure exerted on the conical plug 11. In the present illustration, the pressure is created by a helical compression spring 24 which is seated between the plate 16 and the face of plug 11. The pressure exerted by the spring (or equivalent force-exerting means) may be adjusted by the screw indicated in FIGURE 6 or by a suitable remoteoperated servomechanism, gear drive, etc.

The annular nozzle 15 shown at the right in FIGURE 1, and in elevation in FIGURE 2, is formed by cooperating convergent and divergent surfaces 26 and 27, respectively, which intersect at a circle 28. Such circle 28 comprises the throat of the nozzle and is the downstream end of the interface region 12 between contact elements 10 and 11. The convergent surface 26 is an exterior conical surface formed at the downstream end of conical plug 11, having an apex point indicated at 29. The divergent surface is an interior frustoconical surface formed at the downstream end of the hollow cone 10, such surface 27 terminating in a circular rim 30.

The taper angles of the convergent and divergent surfaces 26 and 27 should be the same, for example approximately forty-five degrees as indicated in the drawing. The location of the surfaces should be such that the apex point 29 and circular rim 30 are disposed in a plane which is perpendicular to the axis of the thruster. Circle 28 is disposed in a second plane perpendicular to the thruster axis, such second plane being spaced a predetermined distance upstream from the first-mentioned plane. As will be described subsequently, the distance between the specified planes may be relatively small, and still achieve a large ratio of discharge (mouth) area to throat area, with consequent optimum expansion effects and with minimized losses in the nozzle.

The described surfaces 26 and 27 are surfaces of revolution about the central axis. However, such surfaces are not necessarily surfaces of revolution. The nozzle may also be defined as an elongated groove which is preferably endless, having walls defining an aerodynamic section which is V-shaped in the present illustration. It is pointed out that the walls which form the nozzle intersect each other at a locus (the nozzle throat) which is spaced substantially outwardly from the axis of the nozzle.

The nozzle may also be defined by rotating the letter V about a central axis, such V being so oriented that the bisector thereof is parallel to such axis. In the present illustration, the rotated V has a common point 29. However, the radius may be made larger (as will be stated subsequently), so that point 29 becomes a surface.

Description of the method, particularly as it relates to the embodiment of FIGURES 14 With particular reference to the embodiment illustrated in FIGURES 1-4, the method comprises effecting flow of high-pressure gas from source 18 through conduit 19 to chamber 17 and thence through the entire interface region 12 between elements 10 and 11 to the nozzle throat 28. The gas then expands through the annular nozzle 15 formed by surfaces 26 and 27, it being understood that such nozzle is disposed in the space surrounding the space vehicle so that a thrust is created to propel the vehicle. The current source 14 is then applied to effect flow of current across the interface region 12, thereby achieving heating of the flowing gas due to the contact resistance between the abutting surfaces.

The pressure created in chamber 17, the bias exerted by spring 24, the voltage and current delivered by source 14, the surface characteristics at the interface 12, and other factors, are correlated to each other in such manner that the melting point of the material (preferably tungsten) forming the elements 10 and 11 is approached at the interface region 12 but is not reached. The melting point should not, however, be so closely approached that substantial gas erosion occurs at the interface due to excessive softening of the metal. It is emphasized that because of the large size and strength of elements 10 and 11, the large gas-flow area, and other factors, the melting point of tungsten may be more closely approached than in other resistance-heating systems, so that a higher temperature may be achieved without resorting to relatively inefficient electric-arc systems.

Because the majority of the resistance between leads 20 and 22 is present at the interface region 12, the majority of the heating occurs at such interface to provide highly efficient heating of the gas, without substantial losses to the surrounding space or surrounding elements. Thus, there is relatively little resistance heating of the elements 10 and 11, which are large in crosssectional current-conducting area. It follows that these elements maintain their strength despite the fact that the temperature adjacent the interface approaches the melting point of tungsten.

The annular nozzle 15 is, as previously indicated, adapted to create a high ratio of discharge (mouth or outlet) area to throat area in a relatively short axial distance. If there were no plug 11 in element 10, so that the region adjacent line 28 were an open hole instead of an annular slit, the flow area through the nozzle throat would be enormously greater than in the present invention. Thus, to achieve the same ratio of discharge area to throat area, the nozzle would have to be much longer than the one described herein, with resulting substantial losses due to friction and radiation.

It is emphasized that, despite the fact that the throat of the present nozzle is greatly constricted in order to permit a relatively short nozzle to achieve a high ratio of discharge area to throat area, the volume of gas flow through the nozzle may be made high. This may be achieved by making the diameter of the nozzle much larger than in the present illustration, the point 29 then being replaced by a circular surface.

The combination of the described annular nozzle with the contact-resistance heater is especially advantageous. One reason for this may be readily understood by considering what would occur if surface 27 and the interface 12 both converged to a common point along the axis of the device. Such an arrangement would be satisfactory relative to continued heating of gas until it reaches the throat of the nozzle, but would be relatively unsatisfactory because the flow volume through the throat would be very small. Furthermore, the very high ratio of discharge area to throat area would not be achieved. On the other hand, if the central plug 11 were cut off to the rear of the throat, in order to achieve a high flow volume, the contact-resistance heating would be terminated substantially before the throat is reached. The efiiciency of the system would be reduced considerably. Therefore, it is the combination of the annular nozzle 15 with the continued contact-resistance heating to the throat that contributes toward the high efiiciency of the present system. It is to be understood, however, that the aboveindicated factors relative to low losses in the nozzle itself, as well as the type of gas (and other factors) as will be described subsequently, are also important to the effectiveness and efiiciency of the thruster.

The maximum efiiciency is achieved by the present thruster, and the maximum specific impulse obtained, when the gas passed therethrough is very light. Thus, if all other factors (such as relating to storage) were relatively equal, the preferred gas would be hydrogen. The lighter gases are preferred because they are stimulated to move at high velocity by the low heat of resistance devices, so that the specific impulse is high. Furthermore, the lighter gases flow readily through the interface region 12. As will be stated hereinafter, the maximum specific impulse is achieved by discharging a dissociated gas through the nozzle, without permitting the gas to recombine prior to complete discharge from the space vehicle.

Embodiment FIGURE 5, and description of additional factors relative to the method In the embodiment of FIGURE 5, the illustrated thruster is identical to that described relative to FIGURES 1-4 except that the spring 24 is replaced by a piston rod 32. Rod 32 is mounted slidably and sealingly through an opening in the plate 16, and extends into a cylinder 33 Where it is connected to a piston 34. A second gas source 35 is connected to the cylinder 33 at the end thereof remote from the nozzle, so that introduction of gas pressure into the cylinder 33 operates through the piston and piston rod to force plug 11 more tightly into the hollow cone 10.

A suitable balancing means 37, which may include a means to vent gas from cylinder 33 when desired, is connected between the two gas sources 18 and 35. The balancing means 37 is adapted automatically to effect the optimum contact pressure at the interface region 12.

The exact contact pressure which should be exerted between the two contact elements and 11 varies in accordance with a substantial number of factors some of which have been indicated above. In general, however, it is desired that the contact pressure be sufficiently light that the voltage developed at the interface region 12 will be substantial, but sufficiently low that there Will be no arcing.

Embodiment of FIGURES 6 and 7 Referring next to FIGURES 6 and 7, an embodiment is illustrated wherein a substantial number of contact elements are so arranged that the contact resistances therebetween are in series-circuit relationship relative to a current source. Thus, the volt-age developed in the system may be made substantially higher than in the previous embodiments, so that the same power can be achieved at a much lower current level.

The apparatus shown in FIGURE 6 comprises an elongated metal casing or housing 41 having a cylindrical chamber 41 therein, such chamber communicating at one end of the housing with a nozzle passage 42 having a conical wall. A substantial number of generally discshaped metal contact elements 43 are disposed in stacked relationship in chamber 41, each such element having a central cylindrical opening 44 therethrough in coaxial relationship with nozzle passage 42. The diameters of the contact elements 43 are smaller than the diameter of chamber 41, so that a manifold annulus 46 is formed around the contact elements.

Gas is fed into annulus 46 from a suitable source 47 which supplies gas to the end of casing 40 remote from the nozzle passage 42. The gas then flows through a passage 48 in an insulating piston disc 49 and into the abovementioned annulus 46. The piston disc is slidable in the chamber so that it may serve to compress the stack of contact elements, such compression action being effected by a compression spring 51 or other suitable pressure device. An adjustment screw 52, for example, may be adapted to vary the degree of compression of the spring 51.

The contact elements 43 and the housing 40 are preferably formed of tungsten and are maintained out of electrical contact with each other except at the region 53 adjacent the nozzle passage. The various contact elements are illustrated as being formed with suitable collar portions 54, and corresponding recesses, so that the spring and piston will maintain the contact elements in alignment despite the fact that the diameters thereof are smaller than the diameter of the chamber 41. Corresponding collars may be formed between the end contact elements and the casing.

A current source 56 is connected to the casing 40 and to the contact element most remote from the nozzle passage. This is effected by means of leads 57 and 58, the latter passing through an insulator 59 and also through the insulating piston 49.

In performing the method with the embodiment of FIGURE 6, the adjustment screw 52 is so regulated that the contact pressure between the adjacent discs 43 will be sufficiently small that a substantial voltage will be developed therebetween, but sufficiently large that no arcing will occur. Gas source 47 is then applied to effect flow of gas into the end of chamber 41 remote from the nozzle, thence through passage 48 into manifold annulus 46, thence through the numerous interfaces between elements 43 and into the central connected openings 44, and thence into the nozzle 42 for discharge to the surrounding space.

Application of current source 56 effects flow of current through the casing 40 and through the series-related stacked discs 43, so that contact heating occurs at each interface between the discs, and also between the end discs and the casing 40, for example at region 53. Such contact heating effects heating of the gas passing through the various interfaces.

In the described manner, any desired voltage may be built up, in accordance with the number of contact elements 43 which are employed. It follows that the current requirements for a given power level may be much lower than in the previous embodiments.

Embodiment of FIGURE 8 FIGURE 8 shows an embodiment in which contactresistance heating is employed in conjunction with are heating to add energy to the gas being passed through a nozzle. In addition, energy is added to the gas by passing the same through a chamber containing the transformer employed to supply alternating current to the electrodes, the losses from the transformer being utilized to raise the temperature of the gas.

The illustrated apparatus comprises an insulating casing 61 having a conical interior wall 62 in which is mounted a conical metal body 63 formed of tungsten or the like,

the relationship being such that the exterior surface of the body 63 is in surface engagement with wall 62. Body 63 is, in turn, provided with a conical opening or passage 64 having an elongated conical plug 66 (also formed of tungsten) mounted therein in surface engagement with the body. Thus, an interface 67 is formed between the plug and the wall of opening 64, for resistance heatmg of current passed therethrough. A compression spring 68 or other suitable means is employed to bias the plug 66 into the opening 64.

Provided in the downstream end wall of casing 61, coaxially of a protruding end portion 69 of plug 66, is a nozzle passage or opening 70. An electrode ring 71 is recessed into the interior wall of casing 61 relatively adjacent such passage or opening 70.

A suitable transformer 72 is connected, by means of leads 73 and 74, to the electrode ring 71 and to body 63, respectively. Transformer 72 is disposed in a casing 77, and is supplied with alternating current from a suitable source 78. A gas source 79 supplies a suitable gas to the casing 77 and thence to the end of casing 61 remote from the nozzle passage 70. The gas then flows through the interface region 67 to the downstream end of casing 61, following which it flows out the nozzle passage 70.

An electric arc, indicated at 81, is maintained between the protruding plug end 69 and the electrode ring 71. Such are may be magnetically rotated, if desired, by means known to the art. Suitable means may be provided to prevent substantial passage of gas through the region between the body 63 and the interior wall 62 of the casing 61.

It is to be understood that the general relationships described relative to FIGURES 6 and 7 may be provided in the embodiment of FIGURE 8, a substantial number of contact discs or other elements then being utilized in series-circuit relationship so that the voltage in the system may be increased.

Proceeding next to a description of the method relative to the embodiment of FIGURE 8, the gas source 79 is applied to pass gas through the transformer casing 77 and thence into the insulating casing 61. The gas then flows through the interface 67 to the downstream end of casing 61, following which it passes through the nozzle 70 to the ambient space. Application of the current source 78 operates through the transformer 72 to apply alternating voltage to the contact body 63 and to electrode 71, the arc 81 being initiated in any suitable manner.

The contact resistance at the interface 67 operates as a ballast resistor for are 81. Thus, since the gas passes through the interface region 67, the heat generated in such region by the ballast resistor is not lost but instead adds to the efliciency of the system. Furthermore, the heat generated by the transformer 72 adds heat to the gas being delivered to the casing 61.

The foregoing detailed description is to be clearly understood as given by way of illustration and example only, the spirit and scope of this invention being limited solely by the appended claims.

I claim:

1. Apparatus for heating a gas, which comprises first and second contact elements in surface engagement with each other whereby an interface region is formed therebetween,

means to pass electric current through said contact elements across said interface region whereby to effect contact-resistance heating of said interface region, and

means to pass gas through said interface region for heating therein.

2. A method of propelling a space vehicle, which comprises providing on said space vehicle first and second solid metal contact elements in surface engagement with each other whereby an interface region is formed therebetween,

passing current through said contact elements across said interface region whereby to effect contact-resistance heating at said interface region, passing a gas through said interface region parallel to the surfaces forming the same whereby to effect heating of said gas, and discharging the resulting heated gas from said space vehicle. 3. Apparatus for effecting heating of a gas, which comprises a stack formed of a substantial number of electricallyconductive contact elements, means to apply a predetermined compressive force to said stack to achieve a desired contact pressure between said contact elements, means to pass electric current in series through said contact elements and thereby across the regions where said contact elements engage each other, whereby contact-resistance heating of said regions is achieved, and means to pass gas through said regions of engagement to effect heating of said gas. 4. A method of heating a gas, which comprises providing a substantial number of solid metal contact elements having corresponding surfaces adapted to stack together in surface engagement with each other, stacking said contact elements to create a substantial number of interface regions therebetween, effecting flow of electric current in series through said contact elements and in series across said interface regions, and passing gas through said interface regions to effect contact-resistance heating of said gas. 5. Apparatus for effecting heating of a gas, which comprises a substantial number of electrically-conductive contact elements each having an opening therein,

said elements having corresponding surfaces adapted to stack together to provide a large number of interfaces, means to maintain said elements in stacked relationship under predetermined pressure and with the openings therein registered with each other, means to supply gas to the peripheral regions of said elements for flow radially inwardly through said interfaces to said registered openings, and means to effect series flow of current through said contact elements to thereby effect contact-resistance heating of said interface regions and thus of said gas,

said gas discharging through said openings. 6. A thruster, which comprises first and second contact elements shaped to define a nozzle of the elongated-groove type, whereby anelongated groove is formed,

the walls of said groove diverging from a central region at the bottom of said groove, said contact elements being in surface engagement with each other along a substantial interface region which extends substantially to said central region at said bottom of said groove, means to pass electric current through said contact elements across said interface region for contact-resistance heating of said interface region, and means to effect flow of gas through said interface region to said groove bottom for discharge through said nozzle, whereby said gas is heated substantially continuously until said nozzle is reached, and whereby said gas discharges from said nozzle without being subjected to excessive frictional and other losses. 7. A method of propelling a space vehicle, which comprises providing a nozzle having a throat and having a discharge portion communicating with the ambient space,

9 passing gas to said throat and thence through said discharge portion to the ambient space, and effecting contact-resistance heating of said gas during substantially the entire time said gas is in the vicinity of said throat whereby to prevent cooling of said said means to effect heating of said gas further comprises a transformer connected to said electrode means to gas prior to discharge thereof through said discharge supply current thereto, and means to pass said gas portion. over said transformer to absorb the heat generated 8. A method of heating a gas prior to discharge thereof therein. through a nozzle, which comprises 16. A thruster, which comprises providing first and second electrically-conductive con- 10 a first contact element formed of tungsten and having tact elements in engagement with each other, an interior conical surface, passing current through said elements and across the a second contact element formed of tungsten and havregion therebetween whereby to efiect contact-resisting an exterior conical surface adapted to be disposed ance heating of said region, in fiatwise engagement with said interior conical applying to said elements suificient pressure to pre- Surface to define a conical interface region therevent arcing across said region but insufiicient presbetween, sure to interfere substantially with flow of gas said conical surfaces defining said interface having through said region, and a common axis, passing gas through said region to thereby effect heatsaid first contact element defining a divergent suring of said gas. face of revolution about said common axis, 9. A method of propelling a space vehicle, which comsaid second contact element defining a convergent prises surface of revolution about said common axis, disposing a plurality of electrically-conductive contact Said divergent and Convergent Surfaces intersecting elements in urface engagement with each other, each other at said interface region and defining passing current through said elements and across the an annular nozzle,

interface region therebetween whereby to efiect nmeans to effect flOW Of gas under high pressure through t p i t h ti f id i t f region, said interface region to said annular nozzle for dispassing a very light gas through said interface region Charge therethfollgh,

and immediately thereafter discharging aid gas from means to bias Said SGCOIld contact element il'ltO said thespace vehicle, first contact element at a predetermined pressure,

said gas being sufficiently light to flow readily and through aid i terfa region for flfi ie t means to pass current through said contact elements tact-resistance heating therein and also being and across said interface region for heating of said suflicienti light to create a high specific impulse gas passed to Said nn l r n zzl upon discharge from said vehicle. 17. The invention as claimed in claim 16, in which 11.0. The invention as claimed in claim 9, in which said said divergent and convergent surfaces are defined by gasis hydrogen rotating substantially straight lines about said com- 11. The invention as claimed in claim 9, in which said 111011 aXiS, gas is ammonia. said straight lines being inclined at substantially 12. A method of propelling a space vehicle, which comequal angles on opposite sides of a line which prises is parallel to said common axis and passes providing a nozzle of the elongated-groove type on a through the intersection of Said divergent and space vehicle and in communication with the ambiconvergent surfaces. ent Space, 18. The invention as claimed in claim 16, in which heating a gas, and said interior conical surface and said exterior conical discharging said heated gas from said vehicle through surface are roughened to facilitate flow of gas said nozzle, said heating of said gas being effected through said interface region. by passing said gas through the interface region be- 19. An electrical plasma-generating device, which comtween a pair of contact elements while effecting flow prises: of current across said interface region whereby to a nozzle element, effect contact-resistance heating of said gas. a rear electrode, 1 AthYuSter,Which comprises means to pass a gas adjacent said rear electrode and nozzle means, thence through said nozzle element, means to P gas through the nozzle Opening in Said electric-circuit means to maintain an electric are be- IlOZZle means, tween said rear electrode and another electrode, l c r d Imam? to maintain an electric a In t thereby effecting electric-arc heating of said gas, and vlcllllty of 52nd nozzle means to heat Sa1d gas Pnor means to effect pre-heating of said gas by the heat to dlscharge thrPugh 851141102116 Openmg and generated in said electric-circuit means at at least means to heat sa1-d gas prior to flow thereof to the one region Spaced fromsaid are, Whemby to improve vicinity of said arc,

said last-named means comprising a plurality of contact elements in surface enthe efficiency of heating of said gas. 20. The invention as claimed in claim 19, in which said electric-circuit means includes a ballast resistor, and said last-named means comprises means to pass said gas in heat-transfer relationship with said ballast resistor to thus absorb heat therefrom prior to further heating of said gas by said arc.

21. The invention as claimed in claim 19, in which said electric-circuit means includes a transformer, and said last-named means comprises means to pass said gas in heat-transfer relationship with said transformer to thus absorb heat therefrom prior to further heating of said gas by said arc.

gagement with each other, means to pass current through said contact elements and across the interface region therebetween, and means to pass said gas through said interface region for contact-resistance heating by the current passed through said contact elements. 14. The invention as claimed in 13 in which said contact elements are arranged in series-circuit relationship relative to said are across a single source of current, whereby the contact resistance between (References on following page) References Cited by the Examiner UNITED STATES PATENTS FOREIGN PATENTS Canada.

OTHER REFERENCES Space Aeronautics, May 1960, pages 42-45, volume 33,

Chemical Engineering Progress, April 1960, pages 60- 63, volume 56, No.4.

Propulsion Systems for Space Flight, 1960, pages 173- 182, McGraw-Hill, New York.

Ballistic Missile and Aerospace Technology, 1961, page 199, volume III, Mororw, Ely and Smith, Academic Press, New York.

10 MARK NEWMAN, Primary Examiner.

CARLTON R. CROYLE. Assistant Examiner. 

9. A METHOD OF PROPELLING A SPACE VEHICLE, WHICH COMPRISES DISPOSING A PLURALITY OF ELECTRICALLY-CONDUCTIVE CONTACT ELEMENTS IN SURFACE ENGAGEMENT WITH EACH OTHER, PASSING CURRENT THROUGH SAID ELEMENTS AND ACROSS THE INTERFACE REGION THEREBETWEEN WHEREBY TO EFFECT CONTACT-RESISTANCE HEATING OF SAID INTERFACE REGION, PASSING A VERY LIGHT GAS THROUGH SAID INTERFACE REGION AND IMMEDIATELY THEREAFTER DISCHARGING SAID GAS FROM THE SPACE VEHICLE, SAID GAS BEING SUFFICIENTLY LIGHT TO FLOW READILY THROUGH SAID INTERFACE REGION FOR EFFICIENT CONTACT-RESISTANCE HEATING THEREIN AND ALSO BEING SUFFICIENTLY LIGHT TO CREATE A HIGH SPECIFIC IMPULSE UPON DISCHARGE FROM SAID VEHICLE. 